General Provisions - Nuclear Power Plant Instrumentation and Control Systems for Safety and Security - page 8

Performance of control functions provides in
general:

decrease in the process of planned or unplanned
disconnection of technological equipment; open-
ing of pilot safety valve of pressurizer if pressure
in the first circuit reached the design limit, etc.
Regulatory functions provide generation and
output of commands for executive I&C systems or
executive elements of technological equipment to
minimize the effect of external disturbances and
/ or transient processes in the controlled object
to controlled parameters of this object. They are
required in the process of power unit operating
modes, in emergencies, design basis accidents
(emergency control) and in the process of post-
accident modes. Regulated parameters are, for
example, neutron and heat power of the reactor,
levels of feed water in steam generators and
regenerative heaters, pressure in the main steam
header, turbine rotating velocity, etc. The regu-
lation purpose can be maintenance of regulated
parameters with a required accuracy on the level
of the specified for them set-point or planned
change of these parameters with time.
Interlocking functions detect failure of normal
operation of technological equipment (overheat-
ing, overload, etc.) and / or conditions required for
its operation (power supply, cooling, oiling, etc.)
and output commands to initiate load decrease or
equipment disconnection, preventing its failure.
Interlocking functions also include cancellation
of fault command execution initiated by other
control systems or operating personnel, which
could cause damage of technological equip-
ment. Interlocking functions have lower priority
comparing to protection functions, except cases,
when a lack of interlocking can lead to heavier
consequences for safety.
Discrete control functions provide generation
and output of commands initiating connection
and disconnection of technological equipment
or elements of pipe mounting, transfer and shut-
down of mechanisms, reactivity control parts
and other actions required to change power unit
mode (operation in cold and hot standby, startup,
power increase, planned shutdown and cooling) or

• Assessment of the state of controlled ob-
ject and environmental conditions.
• Determination of impacts on the controlled
object, which are required to achieve con-
trol purpose.
• Formation and output of commands for
executive elements of technological equip-
ment, which implement control impacts.
• Assessment of achieved control purpose.

Specified actions can be concentrated in one
control I&C system or in several interacting I&C
systems. For example, obtaining of current data
required for performance of control functions can
be obtained by other I&C systems, which perform
monitoring information functions and generate
data for a control system, direct output of com-
mands for executive elements of technological
equipment can be performed а by other (executive)
I&C systems, providing discrete control functions
initiated by commands of the control I&C system.
Protection functions provide timely detection
of failures of design specific operating limits and
/ or conditions of safety operation and output of
commands for executive I&C systems and element
of technological equipment initiating emergency
reactor shutdown, emergency core cooling and
residual heat removal, localization of radioactive
materials and limitation of accidental release.
Protection function has a higher priority compared
to other functions of I&C systems.
Limitation functions provide timely detection
of failures in design specific operating modes
and commands for executive I&C systems or
technological equipment elements, on prohibi-
tion of modifications (increase or decrease) of
specific parameters or initiate their forced return
to the limits of the determined range, considered
acceptable in current conditions. Limitation func-
tions for example include: generation and output
of commands, initiation forced reactor power